The present invention generally relates to tamper evident labels. Specifically, the present invention relates to tamper evident labels incorporating RFID transponders. Multiple adhesive and/or slitted media propagation points are used to ensure that a label with a transponder may not be removed without destroying the transponder operability.
RFID transponders are well known in the art. RFID transponders may be integrated into a label which is then used to affix the RFID transponder functionally to a desired surface, object and or package. RFID transponders integrated into labels are generally designed to be thinner overall and durable enough to withstand an automated insertion process during label manufacture.
However, the high durability of the transponder integrated into the label also allows the transponder to be removed from one object and then, if desired, repositioned onto another object without damaging the transponder. This characteristic should be avoided where the RFID transponder is used, for example, as an anti-counterfeiting device. It is also desirable in many other applications to have an RFID label that is tamper evident, for example, in security applications.
Previous tamper evident RFID labels have been designed and developed using a release layer between the transponder substrate and the printed ink antenna. When the RFID is attached to the substrate a bond is formed which during an attempted removal of the transponder is higher than that of a bond between the transponder carrier film and the printed antenna. Therefore, if the transponder is removed, the antenna will tear/disconnect thereby self-destructing and leaving the RFID inoperative.
A manufacturer using the previous form of tamper-evident RFID labels is required to tune the release layer force and the adhesive for each surface corresponding to different objects/materials which the label will be affixed to.
The release layer in previous tamper-evident transponders must be fine tuned to allow a correct release force between the antenna and a pre-identified substrate. If the adhesive release force is too light, the antenna may not successfully propagate a disabling tear. If the adhesive release force is too high, the label may separate at the substrate level, for example tearing a corrugated box rather than the label. Where the label is removable intact from the package the tamper-evident properties of a label are nullified. Also, the RFID label may be reaffixed, perhaps to a different object, thereby frustrating security and anti-counterfeiting uses. Further, the adhesive typically is selected for a specific footprint size and substrate material. As the footprint size increases, the bond strength increases.
The drawback with this method is that it requires a wide range of different configurations, increasing cost and reducing usability of the RFID label. Therefore, it is an object of the present invention to provide a tamper-evident label which may be used on a wide range of substrates/materials/objects without requiring reconfiguration of the release layer release force or changing the adhesive.
A RFID label with tamper-evident anti-counterfeiting and security capabilities, that in a single configuration is usable with many substrates. The release layer is positioned between the transponder substrate and the printed ink antenna. The RFID label release layer uses a pattern of adhesive whereby different substrate""s cohesive strengths are accommodated. The adhesive pattern accommodates high and low substrate cohesive strength depending on which portion of the label is experiencing separation force. Because the release layer is in contact with the patterned adhesive, when the label is removed the antenna separates from the transponder substrate.
The patterned adhesive may also be combined with propagation slits in the label carrier film. The slits, when stressed, start propagating tears in the label surface ultimately severing the antenna, thereby destroying the transponder.